Agave nectar is a solution while sugar is a solid form. Comparing agave nectar and sugar in the glycemic index is done by weight not actual sugar load therefore the agave nectar is lower because of the dilution factor. Agave nectar is more like a mildly diliuted version of high fructose corn syrup. The glycemic index needs to be understood before using it as a reference to actual sugar content. Too many factors are involved.

Barbara, I beg to differ. Agave nectar has a low glycemic index and is healthier in that regard than most natural and processed sugars, certainly more than refined white sugar from which simple syrup is normally made. White sugar scores 60 or higher on the glycemic index; agave nectar (which is not milky white but pale amber) scores in the low 30s. The nice thing about using agave in some cocktails, especially ones with good acidity lime lime juice is that it adds a bit of texture and mouth feel.